Known means of connecting metallic electrical circuits, such as flexible circuits and terminals on integrated circuits, to conductors on a ceramic substrate, such as indium-tin oxide (ITO) conductors on a glass substrate, include the use of a conductive adhesive, the use of a anisotropic conductive medium pressed between the metallic electrical circuits and the conductors on the ceramic material, and the use of solder.
While each of these means has been used successfully, they each have drawbacks. Conductive adhesives can be susceptible to thermal cycling fatigue, which causes a gradual rise of resistance of the connections, and are typically non-repairable. Anisotropic conductors are often used for connecting a plurality of the metallic conductors arranged in a row to a plurality of the conductors on the ceramic, by pressing the anisotropic medium between the rows of conductors, the pressure induced by backing plates or adhesives. Either approach to achieving the necessary pressure tends to suffer from non-uniformity of pressure, thus leading to non-uniform conductivity of the electrical connections. For making solder connections possible, a technique currently used is to fabricate solder pads on ITO conductors by sputtering three successive layers of materials over the ITO conductors at solder pad areas. The layers are sputtered in the following order: titanium tungsten, nickel, then gold. This process, while providing good solder pads, is expensive.
Thus, what is needed is a low cost means for providing a reliable conductive bond between metallic conductors and ceramic conductors on ceramic substrates.